On my system (Windows Version 10.0.18362.329) it didn’t ask for a reboot but even after rebooting VirtualBox still didn’t work. That’s when I remembered I had enabled the Virtual Machine Platform option in the “Turn Windows Features on or off” section of Programs and Features. Disabling this feature and rebooting allowed Virtualbox VMs to boot without issues.

Here’s how to disable the option through PowerShell with Admin rights: